In data communications over a local telephone subscriber loop where simultaneous or alternating plain old telephone system (POTS) services are present, both digital data and ring signals are transmitted over the same transmission lines. Even though known methods attempt to make the data communications and the POTS communications independent via techniques such as frequency division multiplexing, reliable independence is impractical to achieve. The initiation of a ring signal is unpredictable and will typically cause data transmission errors and disrupt data transmission from the beginning of the ringing cadence, during the ringing cadence, and at least for some duration after cessation of the ringing cadence. Moreover, telephone ring interruption may cause loss of a digital data session due to the long communication interruption.
Some prior art systems have the capability of retransmitting data to a remote modem when communication errors occur. However, in these systems, the remote modem sends a notification to the transmitting modem to indicate that a reception has occurred and to request a retransmission. However, due to the largest and relatively long disturbance of a ringing signal, such notification is often not received by the transmitting modem when a ringing signal is causing the communication error.
Moreover, in some applications where telephone rings occur often, data operation may become impractical due to the frequency of telephone ring interruption. While it is possible to attempt to make the digital data path and the simultaneous POTS path mutually independent, for example, via POTS-splitter filters, this is often practically impossible due to the extremely large amplitude of the interfering signals with respect to the data signals. Therefore, for concurrent digital data communication and POTS communication (where digital data communication may be interrupted from time to time by ring signal requests for POTS service), sustained digital data communication is often not possible during the telephone ringing cadence associated with a request for POTS service.
Thus, a heretofore unaddressed need exists in the industry for providing a system and method for interleaving the transmission of telephone rings and digital data.